Le A C, Musil L S
Vollum Institute for Advanced Biomedical Research, Oregon Health Sciences University, Portland, Oregon, 97201, USA.
Dev Biol. 1998 Dec 1;204(1):80-96. doi: 10.1006/dbio.1998.9030.
The cells of the vertebrate lens are linked to each other by gap junctions, clusters of intercellular channels that mediate the direct transfer of low-molecular-weight substances between the cytosols of adjoining cells. Although gap junctions are detectable in the unspecialized epithelial cells that comprise the anterior face of the organ, both their number and size are greatly increased in the secondary fiber cells that differentiate from them at the lens equator. In other organs, gap junctions have been shown to play an important role in tissue development and differentiation. It has been proposed, although not experimentally tested, that this may be true in the lens as well. To investigate the function of gap junctions in the development of the lens, we have examined the effect of the gap junction blocker 18beta-glycyrrhetinic acid (betaGA) on the differentiation of primary cultures (both dissociated cell-derived monolayers and central epithelium explants) of embryonic chick lens epithelial cells. We found that betaGA greatly reduced gap junction-mediated intercellular transfer of Lucifer yellow and biocytin throughout the 8-day culture period. betaGA did not, however, affect the differentiation of these cells into MP28-expressing secondary fibers. Furthermore, inhibition of gap junctions had no apparent effect on either of the two other types of intercellular (adherens and tight) junctions present in the lens. We conclude that the high level of gap junctional intercellular communication characteristic of the lens equator in vivo is not required for secondary fiber formation as assayed in culture. Up-regulation of gap junctions is therefore likely to be a consequence rather than a cause of lens fiber differentiation and may primarily play a role in lens physiology.
脊椎动物晶状体的细胞通过缝隙连接相互连接，缝隙连接是细胞间通道簇，介导低分子量物质在相邻细胞的胞质溶胶之间直接转移。虽然在构成晶状体前表面的未特化上皮细胞中可检测到缝隙连接，但在晶状体赤道处由它们分化而来的次级纤维细胞中，缝隙连接的数量和大小都大大增加。在其他器官中，缝隙连接已被证明在组织发育和分化中起重要作用。尽管尚未经过实验验证，但有人提出在晶状体中可能也是如此。为了研究缝隙连接在晶状体发育中的功能，我们检测了缝隙连接阻滞剂18β-甘草次酸（βGA）对胚胎鸡晶状体上皮细胞原代培养物（解离细胞来源的单层培养物和中央上皮外植体）分化的影响。我们发现，在整个8天的培养期内，βGA大大降低了缝隙连接介导的荧光素黄和生物素的细胞间转移。然而，βGA并不影响这些细胞分化为表达MP28的次级纤维。此外，抑制缝隙连接对晶状体中存在的另外两种细胞间连接（黏着连接和紧密连接）均无明显影响。我们得出结论，在培养实验中，体内晶状体赤道处特有的高水平缝隙连接细胞间通讯对于次级纤维形成并非必需。因此，缝隙连接的上调可能是晶状体纤维分化的结果而非原因，并且可能主要在晶状体生理学中发挥作用。
